Behavior of gellan in
aqueous-salt solutions and
oilfield saline water
Nurakhmetova Zh.A.*, 1,2Gussenov I.Sh.,
Tatykhanova G.S., 1,2Kudaibergenov S.E. 1,2
1,2
1
Laboratory of Engineering Profile of
K.I. Satpayev Kazakh National Technical
University, Almaty, Kazakhstan
2
Institute of Polymer Materials and
Technology, Almaty, Kazakhstan
*E-mail: [email protected]
Тұзды-су ерітіндісі мен жер
қабат суында гелланның
қасиеттері
1,2
Нурахметова Ж.А.*, 1,2 Гусенов И.Ш., 1,2
ТатыхановаГ.С., 1,2 Кудайбергенов С.Е.
1
Қ.И. Сәтбаев атындағы Қазақ ұлттық
техникалық университетінің инженерлік
профиль зертханасы, Алматы қ., Қазақстан
2
Полимер материалдары және технология
институты, Алматы қ., Қазақстан
*E-mail: [email protected]
Поведение геллана в
водно-солевых растворах и
пластовой воде
1,2
Нурахметова Ж.А.*, 1,2 Гусенов И.Ш., 1,2
ТатыхановаГ.С., 1,2 Кудайбергенов С.Е.
1
Лаборатория инженерного профиля
Казахского национального технического
университета имени К.И. Сатпаева,
г. Алматы, Казахстан
2
Институт полимерных материалов и
технологий, г. Алматы, Казахстан
*E-mail: [email protected]
© 2015 Al-Farabi Kazakh National University
The influence of storage time and temperature on the behavior of low acyl gellan (LAG) was
studied by viscometry and 1H NMR spectroscopy without salt addition. The viscometric results revealed that the effectiveness of salts to enhance gelation of gellan changes in the following order:
BaСl2>CaCl2≈MgCl2>KCl>NaCl. The sol-gel and liquid-solid phase transitions of gellan solutions were
observed upon addition of oilfield water containing 73 g L-1 of alkaline and alkaline earth metal
ions. The effectiveness of salts to induce the separation of liquid and solid phases changes in the
sequence: NaCl>KCl>MgCl2≈CaCl2≈BaСl2. The hydrodynamic behavior of 0.5 wt.% gellan solution injected into the sand pack model with high (20 Darcy) and lower (2 Darcy) permeability is useful to
model the oil reservoirs in the process of enhanced oil recovery.
Keywords: gellan; viscosity; rheology; sol-gel-sol transition; phase transition.
Мақалада вискозиметрия және ЯМР 1Н спектроскопия әдістерімен төмен ацилденген
гелланның (ТАГ) сулы ерітіндісінің ұзақ уақытқа сақталу мерзімі мен температура әсері
тұздардың қатысынсыз зерттелді. Гель түзу нәтижесіне жеке тұздардың әсері келесі қатар
бойынша өзгеретіндігі анықталды: BaСl2> CaCl2 ≈ MgCl2 > KCl > NaCl. Гелланның сулы ерітіндісінің
золь-гель және гель-золь ауысуы сілті және сілтілік жер металлдарының иондары 73 г/л болатын жер қабат суын қосқанда байқалады. Сұйық және қатты фазаға бөліну нәтижесіне жеке
тұздардың әсері келесі қатар бойынша өзгеретіндігі анықталды: NaCl >KCl> MgCl2 ≈CaCl2≈ BaСl2.
Мұнай шығымын арттыру үрдісін модельдеу үшін 0,5% гелланның сулы ерітіндісі қолданылып,
жоғарғы (20 Дарси) және төменгі (2 Дарси) өтімділіктегі құмды модельдің фильтрациялық
қасиеті зерттелді.
Түйін сөздер: геллан; тұтқырлық; реология; золь-гель-золь ауысу; фазалық ауысу.
В работе методами вискозиметрии и ЯМР 1Н спектроскопии изучено влияние времени
хранения и температуры на вязкость водного раствора низкоацилированного геллана
(НAГ) в отсутствие соли. Установлено, что влияние отдельных солей на эффективность
гелеобразования изменяется в следующем порядке: BaСl2> CaCl2 ≈ MgCl2 > KCl > NaCl. Зольгель и гель-золь переходы водного раствора геллана наблюдаются при добавлении пластовой
воды с минерализацией 73 г/л, содержащей ионы щелочных и щелочноземельных металлов.
Влияние отдельных солей на эффективность разделения жидкой и твердой фазы изменяется в
следующей последовательности: NaCl >KCl>MgCl2 ≈CaCl2 ≈BaСl2. Для моделирования процесса
увеличения нефтеотдачи с использованием 0,5%-ного водного раствора геллана были проведены фильтрационные исследования на насыпных песчаных моделях с высокой (20 Дарси) и
низкой (2 Дарси) проницаемостью.
Ключевые слова: геллан; вязкость; реология; золь-гель-золь переход; фазовый переход.
UDK 541.64+678.744
http://dx.doi.org/10.15328/cb640
Behavior of gellan in aqueous-salt solutions
and oilfield saline water
Nurakhmetova Zh.A.*, 1,2Gussenov I.Sh., 1,2Tatykhanova G.S., 1,2Kudaibergenov S.E. 1,2
Laboratory of Engineering Profile of K.I. Satpayev Kazakh National Technical University, Almaty, Kazakhstan
Institute of Polymer Materials and Technology, Almaty, Kazakhstan
*E-mail: [email protected]
1
2
1. Introduction
According to a literature survey, a huge amount of
publications is devoted to polysaccharides, in particular gellan,
which is produced by the bacterium Pseudomonas elodea
and consists of a tetrasaccharide repeating unit of D-glucose,
D-glucuronic acid, D-glucose, and L-rhamnose [1-3]. Review
article [4] comprehensively considers the structure, rheology,
gelation, topology, and application aspects of gellan. The coilhelix conformational and sol-gel phase transitions of gellan
gums induced by temperature, salt addition, pH change etc.
were the main subject of the most research [5, 6]. A series of
publications cover a formation of interpenetrating networks
with participation of gellan and natural polymers [7-9].
It is commonly accepted that gellan gum exhibits a
conformational change from the disordered state (single
chain) to the ordered state (double helix) with decreasing
temperature, and the gelation is considered to be mediated by
the double-helix formation and the association of such helices
enhanced by the presence of mono- and divalent alkaline and
alkaline earth cations. Monovalent counter ions are responsible
for the screening of the electrostatic repulsion between
adjacent molecules and promote coil-helix transition and
association between gellan molecules while divalent ions form
the ionic bonding between two carboxyl groups. It has been
established that the extent of aggregation and effectiveness in
promoting gel formation by addition of ions follows this order:
Cs+ > Rb+ > K+ > Na+ > Li+. This sequence coincides well with
increasing of the ionic radius of cation species. The higher
effectiveness of divalent cations in comparison with monovalent
cations may be attributed to additional crosslinking of gellan
chains due to cooperative binding (or “bridging”) of the
divalent cations between glucuronate residues according to
their ionic radii. Divalent cations seem to bind directly with
© 2015 Al-Farabi Kazakh National University
gellan molecules to form aggregates of gellan helices with the
effectiveness of Ca2+˃Mg2+ [10-13].
The sol-gel technology is one of effective ways to design
materials with definite chemical and physical mechanical
properties. Transformation of sol to gel state proceeds with an
increase of either concentration of disperse phase or under
the action of external factors (concentration of polymer,
temperature, time, pH medium, ionic strength etc.).
Rheological properties of deacylated gellan gel are superior
to those of other common polysaccharide gels such as agar,
κ-carrageenan, and alginate at similar concentrations. According
to these authors, the hardness, brittleness, and elasticity of
gellan gel at 0.5% is comparable to, and its stiffness is much
higher than, 1% K-carrageenan, 1.5% agar, or 4.0% gelatin
gels [14].
Earlier [15] we have demonstrated for the first time
that the sol-gel transition of gellan can successfully be used
for enhanced oil recovery (EOR). The remarkable property of
gellan was plugging of high drainage channels in oil reservoirs.
According to oilfield tests provided at Kumkol oilfield
(South Kazakhstan), the technological effectiveness of an oil
recovery reached 2000 tons of oil per 1 ton of injected gellan
that is comparable with the best results obtained for linear
poly(acrylamide) cross-linked by chromium ions.
In the present paper, we have studied the viscosity,
rheology, sol-gel and gel-sol transformations of low acyl gellan
in the presence of both NaCl, KCl, MgCl2, CaCl2 and oilfield
saline water containing 73 g L-1 of alkaline and alkaline earth
metal salts. The obtained results will be useful to select optimal
conditions of gellan gelation to be injected into oil reservoir for
application in EOR.
Article History
Received: 16 July 2015
Accepted: 3 November 2015
Published: 15 Deсember 2015
64
Behavior of gellan in aqueous-salt solutions...
2. Experimental Part
analyzer (Epsilon 3 SW LTU, PANalytical, Netherlands).
2.1 Materials
Food grade low acyl gellan (LAG) purchased from “Zhejiang DSM Zhongken Biotechnology Co., Ltd.”, China, was used
without further purification. Gellan contained mainly K ion
(17.9 ± 0.088 wt.%). The elemental composition of the gellan
was determined on X-ray fluorescence analyzer Epsilon 3 SW
LTU PANalytical (The Netherlands). Gellan was dispersed in distilled water at room temperature (25 ±1°C) under vigorous magnetic stirring. Gellan concentrations selected for experiments
varied from 0.2 to 1 wt.% on a dry weight basis. Low molecular
weight salts, NaCl, KCl, CaC12 and MgCl2, purchased from JSC
“Reactiv”, Russia, were used without further purification. The
oil field water from “Kumkol” oil reservoir with a density of
1.05 g cm3 and pH 6.68 composed of 22.5 g L-1 of Na+ and K+,
3.8 g L-1 of Ca2+, 0.85 g L-1 of Mg2+ , and 43.9 g L-1 of Cl− ions.
2.2 Methods
The viscosity of aqueous gellan solutions was measured on
the Ubbelohde viscometer at 25±0.1°C. Proton NMR spectra of
gellan were registered on JNM-ECA 400 (JEOL) at 30°C. The total
salinity of oilfield water was determined on SevenCompactTM
S230 (Mettler-Toledo, Switzerland). The elemental composition of oil field water was analyzed with an X-ray fluorescence
3. Results and Discussion
3.1 H1 NMR spectra of gellan
Proton spectra of gellan in D2O represent a set of
resonance lines that are difficult to interpret comprehensively.
Therefore, the proton signals belonging to each saccharide
units were only identified. High frequency signal with 5.08
ppm corresponds to H-1 α-anomer of L-ramnose. The presence
of ramnopiranosol residue is justified by signal at 1.25 ppm
corresponding to protons of methyl radicals. Signals at δ = 4.66
and 4.48 ppm can correspond to 1,4-α- and 1,3-β-glucopiranosol
units, respectively. The presence of glucoronic acid is verified by
downfield signal at δ = 4.64 ppm. Identification of proton signals
of gellan is represented in Fig.1 and Table 1.
3.2 Influence of storage time and temperature.
The influence of storage time on solution behavior of
gellan is shown in Fig.2. The time dependence of viscosity of
gellan at the interval of concentration 0.2-0.5% is similar. The
viscosity has the minimal value at the fifth day of storage, followed
by the increase and further slight changes. Slightly decreasing
viscosity of gellan with time is probably connected with a
destruction of gellan associates stabilized by hydrogen bonds.
Figure 1 – Structural unit of gellan and its H1 NMR spectra in D2O at 30°C
Table 1 – Characteristic chemical shifts of H1 NMR spectra of gellan
Chemical shift, ppm
Fragment of saccharide
5.08; 1.25
1,4-α-L-ramnose
4.66
1,4-α-D-glucose
4.48
1,3-β-D-glucose
4.64
1,4-β-D-glucoronic acid
Вестник КазНУ. Серия химическая. – 2015. – №3(79)
65
Nurakhmetova Zh.A. et al.
Figure 2 – Dependence of the viscosity of gellan on
a storage time
Figure 3 – Dependence of the viscosity of gellan on
a temperature
Figure 4 – Dependence of the viscosity of 0.2% gellan on the ionic strength of the solution adjusted by alkaline and alkaline-earth
metal salts. Arrows point at a gel formation
A viscosity of gellan solutions gradually decreases with
an increase of a temperature (Fig. 3). Initial values of the
viscosity considerably differ at 25°C, however, they more
or less fit together at 50°C. This may be connected with a
gradual disaggregation of macromolecular associates due to
destruction of hydrogen bonds. One can suggest that in oil
reservoir, gellan solution will be stable to biodegradation
during 1 month, however, with a reduced viscosity at high
temperature.
3.3 Influence of one- and two-valent alkaline and alkaline
earth metal ions
According to viscometric measurements, the effectiveness
of salts to enhance gelation changes in the following order:
BaСl2 > CaCl2 ≈ MgCl2 > KCl > NaCl (Fig. 4). This order is in good
agreement with the results presented in [12] found for gellan.
The higher effectiveness of divalent cations in comparison
with monovalent cations may be attributed to additional
crosslinking of gellan chains due to cooperative binding
(or “bridging”) of the divalent cations between glucuronate
residues according to their ionic radii [13,14]. The critical
concentration of salts, expressed as the ionic strength of the
solution, leading to sol-gel and gel-sol phase transitions of 0.2%
gellan solution are summarized in Table 2.
3.4 Influence of oilfield water
Table 2 - Sol-gel and gel-sol phase transitions of 0.2 wt.% gellan solution in the presence of various salts
Salt type
Critical value of the ionic strength inducing the
sol-gel transitiona, (mol L-1)
Critical value of the ionic strength inducing the gel-sol
transitionb, (mol L-1)
BaCl2
0.0045
0.036
CaCl2
0.006
0.036
MgCl2
0.006
0.036
KCl
0.01
0.15
NaCl
0.1
0.20
According to viscometric data; bVisual observation.
a
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Behavior of gellan in aqueous-salt solutions...
Figure 5 – Dependence of the amount of sol (1) and gel (2) fractions of 0.5 wt.% gellan solution upon addition of oilfield water
with a salinity 73 g L-1
One of the remarkable properties of gellan is its ability to
undergo sol-gel and gel-sol transitions in oilfield brine water
of Kumkol oil reservoir containing mono- and divalent cations,
such as Na+, K+, Ca2+ and Mg2+ with a total salinity 73 g L-1.
Addition of 10-30 vol.% oilfield saline water to aqueous
solution of gellan causes the gel formation (sol-gel transition)
while in the presence of ≥ 40 vol.% oilfield saline water,
transformation of gellan from the gel to sol (gel-sol transition)
takes place (Fig. 5). Sol-gel transition of gellan in oilfield water
may be beneficial for extraction of oil from saline reservoirs.
First of all, pumping aqueous solution of gellan into the
injection well will be easy due to low viscosity of polymer.
Secondly, the gel slug that is formed after contacting with
underground saline medium can move to the deep stratum
and can block or reduce the flow capacity of high-permeability
channels without damaging less-permeable hydrocarbon-
productive zones. Consequently, injecting water (water
flooding) should penetrate as much as possible into the
less-permeable zones so that oil can be displaced from these
poorly swept zones.
3.5 Behavior of gellan solution in a sand pack model
It is also interesting to study the flow behavior of gellan
solution in a sand pack model. It is expected that the gellan
solution in the course of injection into oil reservoir will undergo
coil-helix conformation and sol-gel phase transitions. The
sand pack model with absolute gas permeability and pore
volume that are equal to 20 Darcy and 47 cm3 (porosity – 38%),
respectively, was initially saturated with brine water with
salinity of 95 g L-1. The brine saturated sand pack was flooded by
crude oil with viscosity 1.218 mPa s and density – 0.772 g cm-3. As a
result, the initial oil and water saturation became equal to 73.2%
and 26.7% respectively. The temperature of the sand pack
model was kept at 62°C during the whole filtration experiments.
Water flooding was simulated by injection of brine into the
sand pack model under the flow rate of 0.5 cm3 min-1. After
pumping of 2 pore volumes (1 pore volume is equal to 50 cm3)
of water through the model, the oil displacement coefficient
was equal to 49%. After completion of water flooding, the 0.5
wt.% gellan solution under the same flow rate was injected
into the sand pack. The hydrodynamic behavior of gellan solution
within the sand pack model is seen from the dependence of
injection pressure on the pumped volume (Fig. 6).
As seen from Fig. 6a, the injection pressure sharply
increases up to 0.47 MPa after injection of 40 cm3 of gellan
solution, and it dramatically decreases down to 0.2 MPa
after injection of 50 cm3 of gellan solution. Such behavior
of gellan is interpreted as follows. When the gellan solution
penetrates into the high permeable channels (or pores)
it contacts with brine and gelation process is enhanced.
Pore volume is 50 cm3; temperature is 55°C, flow rate is 0.5 cm3 min-1.
Figure 6 – Changing of injection pressure during the filtration of 0.5 wt.% gellan solution
through the sand pack model with permeability of 20 (a) and 2 Darcy (b)
Вестник КазНУ. Серия химическая. – 2015. – №3(79)
Nurakhmetova Zh.A. et al.
Formation of gel particles within the pores decreases the
permeability and increases the injection pressure. Injection of
10-40 cm3 of gellan solution into the sand pack saturated by
brine and oil is accompanied by displacement of oil-containing
liquid (no. 1-4 inset). Accumulation of gel particles inside of high
permeable channels and severe plugging of the sand pack model
takes place between 40 and 50 cm3 of injected gellan solution.
Plugging of high permeable zones of sand pack model by gellan
gel is accompanied by the absence of squeezed out liquid (no.5
inset). Some portion of gellan gel generated inside of the porous
media is displaced out of the model after injection of 50-60
cm3 gellan solution. The breakthrough of gel plug leads to a
sharp decrease of injection pressure together with continuous
displacement of oil and water mixture from the sand pack
model (no. 7-10 inset). The permeability of porous media and
gellan concentration play a crucial role in plugging mechanism.
When the permeability of porous media is extremely high (for
instance, 20 Darcy) the gelation of gellan takes place only once,
causing sharp increase and decrease of pressure. Periodically
increase and decrease of injection pressure (oscillation of
pressure) is observed for the sand pack model with lower
permeability (Fig. 6b). For example, the oscillation behavior of
0.5 wt.% gellan solution was detected inside of the sand pack
model with permeability 2 Darcy. The hydrodynamic behavior of
0.5 wt.% gellan solution presented in Fig.4b may be explained
in the following way. When 0.5 wt.% gellan solution penetrates
into the brine saturated sand pack model, it preferentially
occupies high permeable channels and plugs them (injection
pressure increases). Accumulation of gel particles in high
filtration channels leads to involvement of new channels to be
plugged. When gellan solution finds such channels it flows into
it (injection pressure decreases).
Thus, permanent plugging of different channels by gellan
gel leads to constant redirection of gellan solution to lower and
lower permeable pores. Such step-by-step plugging of high and
67
low permeable channels is responsible for periodic increase and
decrease of injection pressure.
4. Conclusion
Structural unit of gellan consisting of four saccharide units
was identified by H1 NMR spectra. The viscosity of gellan at the
interval of concentration 0.2-0.5% is stable at least during one
month. The viscosity of gellan solutions gradually decreases
with an increase of a temperature due to destruction of hydrogen bonds leading to disaggregation of macromolecular associates. The effectiveness of salts to enhance gelation of gellan
changes in the following order: BaСl2 > CaCl2 ≈ MgCl2 > KCl >
NaCl that is in good agreement with literature data. The sol-gel
and gel-sol transitions of gellan were observed upon addition of
various amounts of oilfield saline water to aqueous solution of
gellan. The hydrodynamic properties of gellan solutions in sand
pack model are determined by permeability of channels. The
flow behavior of 0.5 wt.% gellan solution injected into the sand
pack model of high (20 Darcy) and low (2 Darcy) permeability is
different. When the permeability of porous media is high, the
gelation of gellan takes place only once, causing rapid increase
and decrease of pressure. Periodically, increase and decrease
of injection pressure (oscillation of pressure) was observed for
the sand pack model with low permeability. The brine-initiated
gelation of gellan is perspective for plugging of the high-permeable channels of oil reservoir and as a shut-off agent in polymer
flooding technology.
Acknowledgements
Authors thank the Ministry of Education and Science of the
Republic of Kazakhstan for financial support (Grant No.4410/
GF4 2015-2017).
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Вестник КазНУ. Серия химическая. – 2015. – №3(79)